Side-by-side specifications of the Synology DS109j and DS109+, from official datasheets. Differences are highlighted.
| DS109j | DS109+ | |
| CPU | — | — |
| Cores / threads | — | — |
| RAM (base) | — | — |
| RAM (max) | — | — |
| Drive bays | 1 | 1 |
| Expandable to | 0 | 0 |
| M.2 slots | 0 | 0 |
| Network | 1× Gigabit Ethernet | 1GbE |
| 10GbE | no | no |
| Max raw capacity | — | — |
| Hot-swap | no | no |
| Form factor | Desktop | desktop |
| Released | 2009 | 2009 |
| Power consumption | 26 W / 10 W | 21 W / 12 W |
| DSM at launch | 2.1 | 2.1 |
Pick the DS109+ if you want the faster CPU and the higher RAM ceiling; it is the better choice for heavier file sharing, more users, and generally smoother NAS performance. Both are 1-bay units with no expansion, no 10GbE, and no M.2, so the real deciding factor is performance and memory rather than upgradeability.